This invention relates to a process for the elimination of undesirable materials from epihalohydrin-derived epoxy resins. More particularly, this invention relates to a process for eliminating materials containing hydrolyzable halides and other high molecular weight materials including those containing hydroxyl functionality from epihalohydrin derived epoxy resins.
Epihalohydrins are often used as an ingredient to prepare epoxy resins. Particularly useful in the preparation of epoxy resins is epichlorohydrin. For example, a dihydric phenol (or other active-hydrogen containing material) is often reacted with epichlorohydrin in the presence of a catalyst. The resulting products include the desired epoxy, high molecular weight materials including oligomers, residual epichlorohydrin, and other contaminants containing hydrolyzable chloride, etc. The preparation of pure epoxies is desirable. High molecular weight materials, such as, for example, oligomers or materials containing hydroxyl functionality, may interfere with the epoxy""s performance.
One use for epihalohydrin-derived epoxies is in the electronics area. Some electronic applications where these epoxies are used include, but are not limited to, conformal coatings, high pressure laminations, castings, die attach adhesives, electrical pottings, encapsulations, and underfills. Hydrolyzable halide is a source of free halide in the presence of moisture. Thus, corrosion caused by a halide is a critical issue in the manufacture of electronic devices. Therefore, elimination of hydrolyzable halides is desirable.
Several methods or processes are known for purifying or isolating epoxies. One of these methods is using one or more separation processes such as stripping or distillation. Another method is reacting an alkali metal hydroxide solution or other solvent-based system and water-washing to remove the free chloride or phenolic salts.
Additionally, various methods or processes are known that reduce the amount of hydrolyzable halide in the epoxy product. For example, many methods have been described for the preparation of resins with low levels of hydrolyzable chloride. (See for example, U.S. Pat. No. 4,485,221). However, most of these methods involve extraction with an aqueous base and require organic solvents, which add expense and decrease process efficiency.
Therefore, the need exists for a process of eliminating hydrolyzable halides and other high molecular weight materials from epihalohydrin-derived epoxies that is safe, environmentally-friendly, versatile, efficient, and solventless.
The present invention provides a process for eliminating hydrolyzable halides and high molecular weight materials from epihalohydrin-derived epoxies. This process can be conducted by the epoxy manufacturer, or can be conducted on a commercially sold epoxy to reduce the level of or to eliminate hydrolyzable halide and high molecular weight materials present. The present invention comprises a process for eliminating hydrolyzable halides and high molecular weight materials from epihalohydrin-derived epoxy resins comprising the steps of: a) reacting an epoxy resin comprising materials containing hydrolyzable halides with a base wherein said base is present in a quantity that exceeds the molar equivalent based on the materials containing hydrolyzable halide; b) heating the mixture while agitating; c) neutralizing said heated mixture with carbon dioxide to form a crude product; and d) distilling said crude product using molecular distillation to yield a product.
Another embodiment of the present invention is a process for eliminating hydrolyzable halides and high molecular weight materials from epihalohydrin-derived epoxy resins comprising the steps of: a) distilling an epoxy resin comprising materials containing hydrolyzable halide using molecular distillation to yield an epoxy distillate; and b) reacting said epoxy distillate with a base wherein said base is present in a quantity that exceeds the molar equivalent based on the materials containing hydrolyzable halide.
Another embodiment of the present invention is an epoxy product formed using said contaminant elimination process. The epoxy product formed advantageously has low hydrolyzable halide content. Additionally, the epoxy product can have an epoxide equivalent weight at or near the theoretical value.
Yet another embodiment of the present invention is an epoxy derived from epihalohydrin that has low hydrolyzable halide content and that does not contain high molecular weight material.
The process of the present invention is solvent-free, relatively inexpensive, versatile, and environmentally-friendly. Moreover, the process of the present invention can be carried out using standard manufacturing equipment and in high volume.
The process of the present invention can be done in batch or as a continuous process.
The present invention provides a process for eliminating undesirable materials from epoxy resins that are derived from epihalohydrin. These undesirable materials or by-products are defined herein as including materials comprising hydrolyzable halides (such as, for example, hydrolyzable chloride, hydrolyzable bromide, or hydrolyzable iodide) and in some epoxy resins high molecular weight materials. Hydrolyzable halides are halide releasing materials. High molecular weight materials are defined herein as dimers and other materials having a molecular weight greater than the dimer. These high molecular weight materials can be oligomers that can contain hydroxyl groups. Other high molecular weight materials include, but are not limited to, reaction by-products, polymerized epoxies, phenolic salts, etc., and mixtures thereof. Examples of some high molecular weight materials that may be eliminated from some epoxy resins include, but are not limited to: 
The process of the present invention has many advantages. For example, this process is a relatively inexpensive procedure for preparing epoxy resins that contain low levels (i.e., preferably 0.1 ppm to 100 ppm, more preferably less than 10 ppm, and most preferably less than 1 ppm) of hydrolyzable halide.
The epoxies of the present invention have an epoxide equivalent weight at or near the theoretical value expected for the specific monomer. Prior to the present invention, low molecular weight halide epoxies such as EPON(trademark) Resin 828 (and its high purity version EPON(trademark) Resin 825), available from Shell Chemical Company, Houston, Tex., is disclosed as having an epoxide equivalent weight of 185-192 (175-180 for EPON(trademark) Resin 825) whereas the theoretical epoxide equivalent weight is 170. (See Shell Resins, SC:235-96.828, October 1996 and Technical Bulletin, Shell Chemical Company SC:235-88.825 January 1992). Whereas, using the present invention, starting with EPON(trademark) Resin 828, an epoxide equivalent weight of 170 is obtained. The method used to obtain the epoxide equivalent weight is set forth in Example 1.
Additionally, the process is non-extractive and thus can be and is solventless. The process is run at 100 percent solids with only a small amount of base being added. Thus, the process is more environmentally-friendly than processes requiring solvents. There are no residual solvents in the epoxy product and therefore no outgassing. Further, this process is a non-solvent and chemical reagent waste generating process. If the high molecular weight materials that are eliminated are used, then the process of the present invention can be non-waste generating.
The process of the present invention is versatile. To purify different epoxy resins, one only needs to change the base in light of the starting epoxy resin. Therefore, the equipment, etc., can remain the same that helps to reduce cost. Further, the required equipment is readily available in the chemical industry.
The process advantageously eliminates oligomers and other high molecular weight materials including those high molecular weight materials containing hydroxyl groups that may not be desirable. Side reactions caused by contaminants are substantially or all-together eliminated. This may improve optical clarity and lower the molecular weight that affects the Theological properties of the epoxy and the resultant glass transition temperature of the cured epoxy. Depending on the curative employed, this elimination of by-products containing hydroxyl groups may provide enhanced pot life for the epoxy resin, which is advantageous in many applications.
Epoxy-resin
The epoxy resin that is purified using the present invention includes any epoxy resin that is derived from epihalohydrin or that contains hydrolyzable halides. Further, this epoxy resin must be distillable using molecular distillation. Therefore, the epoxy resin must not decompose during the distillation process.
The epoxy resins suitable for the present invention can contain materials containing hydrolyzable halides. For example, epoxy resins having hydrolyzable halide contents of 10,000 ppm and epoxy resins having hydrolyzable halide contents of 150 ppm are suitable for the process of the present invention. Further, the epoxy resins of the present invention may include other high molecular weight materials that can contain hydroxyl groups.
One example of an epoxy resin suitable for the process of the present invention can be prepared as illustrated below. 
This epoxy resin contains the desired bisphenol A epoxy product, as well as 1,2 chlorohydrin (containing hydrolyzable chloride), and 1,3 chlorohydrin.
Examples of epoxy resins useful in the process of the present invention include, but are not limited to, bisphenol A-epichlorohydrin epoxy resins, bisphenol F-epichlorohydrin epoxy resins, aliphatic mono glycidyl ethers, aliphatic diglycidyl ethers, aliphatic multifunctional glycidyl ethers, and aliphatic glycidyl esters.
Examples of useful bisphenol A-epichlorohydrin epoxy resins include, but are not limited to, EPON(trademark) Resins 825, 826 and 828, available from Shell Chemical Company, Houston Tex., D.E.R.(trademark) 330, 331, and 332, available from Dow Chemical Company, Midland, Mich., and ARALDITE(trademark) GY 6008, GY 6010, and GY 2600, available from Ciba Specialty Chemicals, Brewster, N.Y.
Examples of useful bisphenol F-epichlorohydrin epoxy resins include, but are not limited to, EPON(trademark) Resin 862, available from Shell Chemical Company, Houston, Tex., and ARALDITE(trademark) GY 281, GY 282, GY 285, PY 306, and PY 307, available from Ciba Specialty Chemicals, Brewster, N.Y.
Examples of useful mono, di and multifunctional glycidyl ether resins include, but are not limited to, HELOXY(trademark) Modifier 107 and HELOXY(trademark) Modifier 48, available from Ciba Specialty Chemicals, Brewster, N.Y., and EPON(trademark) 1510, available from Shell Chemical Company, Houston Tex.
Materials having groups that are sensitive to hydrolysis by strong bases such as epoxies having ester linkage are also suitable for the process of the present invention. For example, CY(trademark) 184, available from Ciba Specialty Chemicals, Brewster, N.Y., is suitable for the process of the present invention.
Base Treatment
The process of the present invention comprises the step of treatment of or the reaction of the epoxy resin with a base. The base is present in an amount that exceeds the molar equivalent based on the materials comprising hydrolyzable halide. This amount depends on the starting epoxy resin. For example, if no other acids are present, a theoretical amount of base can be used based on the ppm of hydrolyzable halide. In other situations, for example, 100 percent to 200 percent base is required.
The epoxy resin may be combined with a base at room temperature to form a mixture or in other situations, the epoxy resin may be pre-heated. Thus, the heating and agitation step may occur prior to and during the reaction with the base, simultaneously with the base treatment step, or after the base is added to the epoxy resin. This order is dictated by the starting epoxy resin.
The selection of the base depends upon the starting epoxy resin. Examples of suitable bases useful in the process of the present invention include, but are not limited to, hydroxides such as potassium hydroxide in water, sodium hydroxide, and lithium hydroxide, hydrides such as lithium hydride, sodium hydride (optionally in mineral oil), and potassium hydride, alkoxides such as primary, secondary, and tertiary (e.g., potassium t-butoxide in THF) alkoxides such as sodium ethoxide, carbonates such as potassium carbonate and sodium carbonate, and quaternary ammonium salts.
Generally, the base strength and the temperature are such that the halohydrin closes to the epoxy and under which the epoxy does not polymerize. For example, in one case for an epichlorohydrin-derived epoxy resin, potassium t-butoxide in THF was suitable at 25xc2x0 C., but the resin polymerized at 70xc2x0 C.
The use of non-nucleophilic bases such as sodium hydride are believed to have the advantageous effect of closing the halohydrin without reacting appreciably with other base (hydrolytically) sensitive functionality such as esters. Without being bound by theory, the following is believed to occur: 
If a non-nucleophilic base is used, the process of the present invention preferably comprises the following steps: (a) distilling an epoxy resin comprising materials containing hydrolyzable halide using molecular distillation to yield an epoxy distillate; and (b) reacting said epoxy distillate with a base wherein said base is present in a quantity that exceeds the molar equivalent based on the materials containing hydrolyzable halide.
The initial distillation step removes moisture along with high molecular weight materials containing hydroxyl functionality. The product can either be neutralized with water and carbon dioxide to remove residual sodium hydride before distillation or can be distilled directly without neutralization.
Heating the Mixture while Agitating
The mixture is heated to a temperature suitable for reaction of the halohydrin to form the epoxy while agitated. For example, the mixture may be heated using a heat mantel. Generally, the mixture is heated between 20xc2x0 C. to 200xc2x0 C. for 1 minute to 12 hours. However, the temperature and time depend upon the starting epoxy resin, base strength and solubility, the catalytic activity of the base towards epoxy polymerization, and commercial viability.
This heating and mixing can occur after the epoxy resin and base are combined, prior to and during the base treatment step, or simultaneously with the addition of the base and base treatment step.
The mixture is usually heated to alter the viscosity, which in turn helps the dispersion of the base.
Neutralization of the Mixture
The heated mixture is then neutralized, if required, using carbon dioxide to form a crude product. With the hydrides, this neutralization step may not be required. Optionally, at this point, residual salts may be removed from the crude product by filtration.
Distillation
Next, the crude product is isolated by molecular distillation to yield the product. For example, a rolled film evaporator or wipe film evaporator may be used. With a rolled film evaporator, the crude product is distributed across a vertical heated surface by an efficient, self-cleaning roller wiper system into a uniform thin film. The evaporated material travels a short distance to an internal condenser. A lower vacuum pressure is used with low operating temperatures. (See UIC Inc., xe2x80x9cShort Path Vacuum Distillation from Laboratory to Productionxe2x80x9d, 1997). With a wipe film evaporator, a wiper is used instead of the self-cleaning roller wiper.
The distillation conditions depend on the boiling point of the crude product.
Noncondensible materials that may be in the starting materials, i.e., the epoxy resin, are removed during molecular distillation.
Product
The yielded epoxy product has low levels of hydrolyzable halide, i.e., preferably from 0.1 to 100 ppm, more preferably less than 10 ppm, and most preferably less than 1 ppm.
The yielded product is preferably free of high molecular weight materials. High molecular weight material-free is defined herein as having no dimers and materials having higher molecular weight than the dimer. The epoxide equivalent weight is at or near the theoretical epoxide equivalent weight (i.e., within 2 percent, preferably within 1 percent of the theoretical epoxide equivalent weight).
The epoxy product of the present invention has a higher cured glass transition temperature than the less pure version, which is advantageous. The epoxy product of the present invention is also more predictable due to product consistency. The viscosity is lower than the less pure version of the same epoxy resin. There is no residual base in the epoxy product, which is advantageous. Residual base may inhibit cationically cured epoxies. Other low hydrolyzable halide epoxy resins such as EPON(trademark) Resin 1462, available from Shell Chemical Company, which have some residual base are described as having a yellow color (a Gardner Color Scale value of less than 3). The epoxy product of the present invention is colorless. For example, using the Gardner test (ASTM D1544-80), the Gardner Color Scale value is less than 0.1 for purified EPON(trademark) Resin 828.
The process of the present invention can be batch or continuous.
Application
The epoxy products of the present invention are suitable in optical applications where clarity is an important property. As indicated above, a low Gardner Color value is obtainable.
The epoxy products of the present invention are suitable as a primer for other epoxy materials for aircraft and automotive applications where corrosion resistance may be important. Additionally, these epoxy products may be particularly useful as either a primer or adhesive on other metallic surfaces where corrosion is an issue.
The epoxy products of the present invention are also particularly suitable for high temperature applications where a high glass transition temperature is desirable.